Cu—Zn-based alloys are excellent in workability and have been widely used in various fields. With regard to Cu—Zn-based alloys, zinc base metal is generally more inexpensive than copper base metal. Therefore, material cost thereof can be reduced by increasing a zinc content. There exists a problem, however, that zinc element present in copper results in significant deterioration in corrosion resistance. In particular, when a copper alloy having an increased zinc content is used for a fastening material which is embedded on a base fabric through cold working, there has occurred a problem of season cracking of the material due to residual work strain.
Japanese Patent No. 4357869 discloses a technique in which an alloy contains elemental additives, such as Al, Si, Sn and/or Mn, and is surface-treated by means of shot-blasting or the like to be provided with compression stress in order to enhance season cracking resistance.